1. Field of the Invention
The present invention relates to arterial blood collection syringes. More particularly, the present invention relates to a one-piece plunger rod for efficient use of an arterial blood collection syringe.
2. Description of Related Art
Arterial blood collection syringes are used for withdrawing and collecting arterial blood samples from the body of a patient. Once the blood sample is collected, it is subjected to diagnostic analysis for gases, electrolytes, metabolites, and other elements that are indicative of a condition of a patient. Various types of syringes have been devised for collecting arterial blood samples, which mainly comprise elements from a hypodermic syringe, i.e., a plastic or glass syringe barrel, a sealing elastomeric stopper, and a plunger rod. Additionally, certain arterial blood collection syringes include a self-sealing filter that allows passage of air out of the syringe during blood collection, while still preventing the passage of blood. This latter type of syringe having a filter allows for an anaerobic arterial sample to be collected without the need to aspirate the syringe, as is required with a syringe having a plunger rod and a plunger stopper.
Typical arterial blood collection syringes include a two-piece plunger rod assembly comprised of an elastomeric sealing stopper attached to a plunger rod. The sealing stopper and plunger rod must be assembled together in a separate operation prior to assembly with a syringe barrel. In addition, a silicone lubricant is usually used on the interior wall of the syringe barrel to facilitate easy slidable movement of the elastomeric sealing stopper against the interior wall of the syringe barrel. Such syringes typically involve an active step for obtaining a blood sample. For example, a needle connected to such a syringe accesses a patient's blood vessel, and the syringe is thereafter aspirated by drawing the plunger rearwardly within the syringe barrel so as to draw a blood sample into the syringe barrel for analysis. U.S. Pat. No. 5,314,416 to Lewis et al. discloses a low friction syringe assembly having a typical two-piece plunger rod and a plunger tip assembly.
Arterial blood samples can also be obtained passively through the use of a syringe having a plunger with a porous filter to collect blood by way of the blood pressure of a patient from whom the blood is being collected. In such a syringe, the plunger mechanism is typically hollow, and includes a porous filter therein. A separate elastomeric sealing stopper is typically attached to the front end of the plunger mechanism for sealing within the syringe barrel, with air channels in the stopper for air passage through the filter. In use, the plunger is set at a certain position against a graduated scale of the syringe barrel, so that the desired volume of the sample to be collected is represented by the cavity within the syringe. Once a blood vessel of a patient is accessed by an appropriate needle attached to the syringe, arterial blood will fill the syringe under its own pressure. As the cavity within the syringe fills, air within the syringe is allowed to escape from the syringe by way of a gas permeable filter. When the blood sample contacts the filter, the filter seals, thereby preventing escape of blood and ingress of air and other contaminants into the collected sample. U.S. Pat. No. 4,821,738 to Iwasaki et al. discloses an arterial blood gas syringe including a typical two-piece assembly for use. The arterial blood gas syringe is comprised of a plunger rod and an elastomeric sealing plug having channels formed in an upper surface for use in removing air as arterial blood is received in the syringe. The channels extend in a generally radial direction and converge near the center of a sealing plug to allow the passage of air to and through a filter element contained within the sealing plug. U.S. Pat. Nos. 5,377,689 and 5,529,738, both to Mercereau, disclose a sampling syringe including a plunger cap having an air permeable filter attached to a plunger rod, which is in slidable communication with the inner wall of a syringe barrel.
The separate rubber sealing stopper on the plunger in such assemblies provides an effective seal to contain the blood sample within the syringe. However, while such syringe assemblies are useful, the separate rubber sealing stopper typically requires a silicone lubricant for sliding movement within the syringe barrel, and further requires costly manufacturing and assembly steps. Accordingly, there is a present need for an arterial blood collection syringe which is inexpensive to manufacture and easy to assemble, and which is simple to operate.